Process of manufacturing cellulose acetate



N0v.1o1925. j 1,560,620

A.' F. SULZER PROCESS OF MANUFACTURING CELLULOSE ACETATE' Filed Jan. 2 8. 19:25v

v A TT ORNEY ParentedNov. 10,1925.

UNITED vSTATI-:s PATENT OFFICE.

ALBERT l'. BULZIIB, OF ROCHESTER, YORK, ASSIGNO TO EASTIAN KODAK COI- PAN?, OF ROCHESTER NEW YORK, A CORPORATION 0F NEW lYORK.

PROCESS OF IANUI'ACTBING GELLULOSE AGETA'ILIE.4

"appuoao 'area navman-issu. 'serial 1ra-ases:

` citizen of the United States of America, re

siding at Rochester, in the lcounty of Monroe and State of New York, have invented cler-l tain new and useful Improvements in Processes of Manufacturing Cellulose Acetate, of which the following is a full, clear, and exact specification.

This invention relates4 to processes of Inanufacturing cellulose acetate, and more particularly to the recovery of valuable materials during such processes.' One object of the invention is to lessen the cost of such manufacture. Another object of the invention is to provide a simple, rapid, and 1nexpensive process for recovering acetlc values, such als acetic acid andv acetic anhydride, from cellulose acetate reaction mixtures. Still another object of the invention is to provide a process in which said acetic values can be recovered in a comparativel pure condition. Other objects will herelnafter appear.

In theaccompanying drawing the single figure isa diagrammatic side elevation, partly in vertical section, showing one form o f apparatus in which my process may be carried out, the relative sizes of the elements being exaggerated for the sake of clearness.

In the manufacture of cellulose acetate acetylating agents act on cellulose in the presence of catalysts. The reaction mixture may, for' instance, initially contaln cellulose, acetic anhydride, acetic acid and a solid or liquid catalyst, such as sulfuric acid. The mass Will, of course, contain the products of the reaction as the latter proceeds. A typical example of this general type is given in U.` S. Reissue Patent No. 12,637, Miles, Apr. 23, 1907. During the course of the reaction chloroform-soluble cellulose 'acetate is first produced. Then a hydrolyzing mixture containing a small, but adequate amount of water, is introduced, so as to convert the cellulose acetate into the acetone-soluble species. Any excess or unused acetic'anhydride which is' present at the end of the chloroform-soluble stage is converted into acetic acid by the addition of water. It is convenient to use suiicient water in the hydrolyzing mixture to convert the excess acetic anhydride into acetic acid and cooperate4 in the hydrolysis.

At the end of the chloroform-soluble stage there are present'in the reaction mixture valuable amounts of acetic values, such as acetic anhydride and acetic acid (and in some cases' acetyl chloride). But where the reaction mixture is carried to the acetonesoluble sta e, the acetic values will be in the form o acetic acid. These acetic values, because of their high cost, have a very important bearing upon the cost of the cellulose acetate which 1s produced. If they are not recovered, the loss per pound of cellulose acetate produced is, undesirably high. It

is, therefore, very desirable to recover them inexpensively and 1n a conditlon in which they can be used agalnfor further acetylation. Thus the cost per pound of the product`- may be very much cheapened.

Where these acetic values have been washed away from the finished cellulose acetate, the resultant dilute solutions are diilicult to treat, in order to recover the values. Evaporating operations and chemical reaction steps have been found to be undesirably complicated or expensive.

- Acetic values have also been recovere from the reaction mixture by taking them up in a gaseous vehicle, such as air, and then' recovering the vapors from the vehicle, as by condensation. This operation is lgenlerall conducted at approximately atmospheric pressure.

I have found, however, that the recovery of the acetic values can' be effectively carried out by dstilling them from a reaction mixture under ressures lower than atmospheric pressure. n the preferred form of my invention the reaction mixture is kept thor- It is well known that if an acetic acid reaction mixture be heated to a high temperature for a substantial length of time, the cellulose acetate will be adversely alfected. If' it be maintained,`for example, at 1189 C., the' boiling point` of acetic acid at atmospheric pressure, for several hours, it may-become entirely unsuitable for film manufacture. By using a relatively strong vacuum during the distillation, the boiling point of acetic acid is lowered to such a polnt that The distillation may be carried Vout inv many kinds of apparatus, the one shown 'in the drawing being merely illustrative of a useful form. Of course, all of the parts ofy the apparatus,'which contact with the corrosive materials, are made of adequatelyref.y sistant materials usually employed forthat purpose. The receptacle 1 into which 'the cellulose acetate reaction mass 2A isloaded through any suitable opening), normally.

closed by an air-tight cover 4, is surrounded by a heating jacket 5 in which a suitable heating fluid, such as hot water or steam maybe circulated in the way customary in this art. At the bottomof receptacle `1 is a removable closure 6 which facilitates'the rcmoval ofthe contents when the' distillation is completed.v The reaction mixture 2 is driven from power shaft 9 through -gears 10.1- The' ace above the reaction mixture 2 in receptabclle 1 is connected through ,a pipe 11 with a condensing worm 12 in the cooling chamber 13, this Worm being connected at the bottom by pipe 14 with receptacle 15, in which the recovered acetic values are collected. At the bottom of receptacle-15 is a pipe 16 controlled by a valve 17,1through which the recovered values may` bey drawn od'. At the to of receptacle 15 there is a pi e 18 contro led by a valve 19, said pipe 18 ing connected with anyY known, or preferred means (not shown) for maintaining subatmospheric pressure in the above described apparatus. This means Jmay be one that maintains a very high vacuum,its eil'ect bev ing stepped vdown by valve 19, or it may include devices which are driven at various Speeds, so as to regulate the vacuum effect.

lt will be understood, of course, that all of the hereinabove described parts are' in a substantially air-tight condition during the distillation. y y

In use, a charge of reaction mixture (say g one in which cellulose acetate is in the chloroform-soluble state, or in the acetone-soluble state, in accordance with the above cited Miles reissue patent) isloaded into receptacle 1 and vagitated by means of rotating blades 7. lt is alsoheated by circulating a warming fluid in jacket 5. While the temperature may vary over quite a range, it is desirable, as stated above, to avoid prolonged -use of any such temperatures as 118 C. By wa of example, temperatures of 40 C. to may be employed.. The vacuum is maintained through connecting pipe 18,.- and the drop below atmospheric pressure is, of course, regulated according to the tem perature to which the reaction mixture 2 vis heated from the jacket 5. The higher the temperature, the. more nearly can` the pressure approach .toward atmospheric. When the temperatures range from 40 C. to 80 C., for example, I prefer to use a vacuum of from`35 to 202 mm. of mercur 'In practice the vacuum can begradually increased' until asatisfactory evolution of'vapors .of acetic -also be varied. But it should not be so low as to vcause solidicationof acetic values in the worm. A temperature of 15.5 C. has been found useful where there is a slight amount of water present, because it enables satisfactory condensation to take place with-A out cloggingthe condenser. Moreover, it keeps the loss of acetic values through pi e -18 at` a minimum. If necessary, receptac e 15 may have lieat-insulated.walls, or it may be artificially cooled byf;`any suitable or preferred means (not shown)r." l thoroughly agitated by blades 7 on shaft 8, l

It is preferable to carry the distillation and agitation of reaction mixture 2 until the flatter becomes a powdery or granular mass.

When in this condition, its removal from receptacle 1, upon opening closure 6, is facilitated. This powder or granular mass is in condition for rapi and uniform further treatment by reason of its very large aggregate surface. In other words, the powder has enormous surface relative toits mass, unlike the viscous liquid or flowable mixture from which it is preferably prepared.

, Having thus described my invention, what 'l claim as new and desire to secure by Letters Patent is:

noo4

` 1. In the process of manufacturing cellulose acetate, the steps of heating, under a vacuum, a cellulose acetate reaction mixture containing vvolatile acetic values to evolve vapors of said values at a temperature bel'oW tli'e one at which the cellulose acetate is' degraded, and removing and liquefying said vapors. l

2. In the process of manufacturing cellulose acetate, the steps of heating to a temperature below 118 C. a cellulos acetate-reaction mixture containing acetic acid, maintaining the pressure thereof below atmospheric pressure' during -said heating to rapidly evolve vlvapors of acetic acid from Said mixture, and condensing said vapors separate from said mixture..

-3. In the process of manufacturing cellulose acetate, the steps of heating to a temperature between 40 C. 'and 80 C'. a flowable cellulose acetate reaction mixture containing volatile acetic values, keeping the Vpressure thereof below atmospheric pressure during said heating to rapidly evolve vapors of said acetic values from said mixture, and removing and condensing said vapors. the operations of said steps being continued until Vthe remainder of said mixture reaches a solid state.

4. In the process of manufacturingcellulose acetate, the steps of heating, under a vacuum, a .cellulose acetate reaction mixture containing volatile acetic values to evolve vapors osaid values at a temperature below the one at which the cellulose acetate is degraded, bringing freshV portions of said mixture to the surface thereof during said heating to assist the evolution of said vapors, and removing and liquefying said vapors.'

5. In the process of` manufacturing'cel- 'lulose acetate, the steps of heating to a temperature below- 118 C. a cellulose acetate reaction mixture containing acetic ac id, agitating said mixture and maintaining the pressure in the space above said mix ture below atmospheric during said heating and agitating to rapidly evolve vapors of acetic acid froml v saidv mixture, and conmixture.

.6. In the process of manufacturing cellulose acetate, the steps of heating to a temperature between 40.. C. and 80 C. a flowable cellulose acetate reaction mixture consaid evolution being continued until the re mainder of said mixture becomes a mass of relatively small particles.

Signed at Rochester, New York this 20th '35 day of January 1925.

, ALBERT F. SULZER.

densing said vapors separate ,from said 20 

